The present invention relates to an air cycle air-conditioning apparatus employing air as a refrigerant and, more particularly, to an efficiency improving scheme.
Cooling apparatus of the air cycle type in which air serves as a refrigerant have been conventionally known in the art. For example, there is disclosed in Japanese Unexamined Patent Gazette No. S62-102061 one type of air cycle cooling apparatus. This type of cooling apparatus includes a compressor, a heat exchanger, and an expansion device. That is, air is drawn into the compressor where the air is compressed. The compressed air is cooled in the heat exchanger and thereafter expanded in the expansion device, for obtaining low-temperature air of low temperature. In the cooling apparatus of the aforesaid Patent Gazette, the cooling air thus obtained is used for achieving cooling of the inside of a room. Further, in the cooling apparatus, the low-temperature air expanded in the expansion device is sprayed with water so that the -temperature of the low-temperature air is lowered to a further extent by evaporation of the water for enhancing cooling capacity.
However, in the aforesaid conventional cooling apparatus, cooling of air compressed in the compressor is carried out by heat exchange with outside air. If outside air temperature rises to as high as 35 degrees centigrade in summer, it is impossible for the cooling apparatus to lower the temperature of the compressed air beyond about 40 degrees centigrade. Accordingly, in order to ensure cooling capacity even when outside air temperature is high, the compression ratio of the compressor must be increased. As a result, compressor driving power should be increased, giving rise to the problem of poor cooling efficiency, i.e., low COP (coefficient of performance).
Bearing in mind the above drawbacks with the prior art, the present invention was made. Accordingly, an object of the present invention is to provide an improved COP while at the same time maintaining the cooling capacity of an air cycle air-conditioning apparatus.
In the present invention, the temperature of cooled, compressed air is lowered and compressor driving power can be reduced while maintaining cooling capacity.
More specifically, the present invention discloses a first solution means which is directed to an air-conditioning apparatus for cooling room air by an air cycle employing air as a refrigerant, thereby performing air-cooling. The air-conditioning apparatus of the first solution means comprises a compressor (21) which draws in at least air in a room for compressing the drawn room air, a cooling means (30) which subjects the compressed air compressed in the compressor (21) to heat exchange with exhaust air expelled from the room for cooling the compressed air, and an expansion device (23) which provides-expansion of the compressed air cooled by the cooling means (30), wherein low-temperature air, cooled by the expansion in the expansion device (23), is delivered to the room.
Further, the present invention discloses a second solution means according to the first solution means in which a moisturizing means (41) is disposed which supplies moisture to the exhaust air that is delivered to the cooling means (30) for pre-cooling the exhaust air.
Further, the present invention discloses a third solution means according to the first solution means in which a moisturizing means (42) is disposed which supplies moisture to the exhaust air so that cooling of the compressed air is performed making utilization of a latent heat of vaporization of water in the cooling means (30).
Further, the present invention discloses a fourth solution means according to the second or third solution means in which, when the exhaust air is expelled from the cooling means (30), each moisturizing means (41, 42) supplies a specified amount of moisture to the exhaust air so that the exhaust air has a relative humidity in a range from not less than 80% to less than 100%.
Further, the present invention discloses a fifth solution means according to the second or third solution means in which each moisturizing means (41, 42) supplies moisture to the exhaust air through a moisture permeable membrane transmittable to moisture.
Further, the present invention discloses a sixth solution means according to the first solution means in which a demoisturizing means (22) is disposed which has a separation membrane and the separation membrane is formed such that water vapor in the air is allowed to pass therethrough from a high partial pressure of water-vapor side to a low partial pressure of water-vapor side thereof, for separation of water vapor contained in the compressed air without causing the water vapor to undergo condensation.
Further, the present invention discloses a seventh solution means according to the sixth solution means in which a depressurizing means (36) is disposed which provides depressurization of one of the sides of the separation membrane in the demoisturizing means (22) so as to ensure a difference in partial pressure of water-vapor between both the separation membrane sides.
Further, the present invention discloses an eighth solution means according to any one of the second to fifth solution means in which a demoisturizing means (22) is disposed which has a separation membrane and the separation membrane is formed such that water vapor in the air is allowed to pass therethrough from a high partial pressure of water-vapor side to a low partial pressure of water-vapor side thereof, for separation of water vapor contained in the compressed air without causing the water vapor to undergo condensation.
Further, the present invention discloses a ninth solution means according to the eighth solution means in which a depressurizing means (36) is disposed which provides depressurization of one of the sides of the separation membrane in the demoisturizing means (22) so as to ensure a difference in partial pressure of water-vapor between both the separation membrane sides.
Further, the present invention discloses a tenth solution means according to the sixth or eighth solution means in which the demoisturizing means (22) is formed so that one of surfaces of the separation membrane is brought into contact with the compressed air whereas the other of the surfaces is brought into contact with the exhaust air, whereby water vapor contained in the compressed air will travel to the exhaust air.
Further, the present invention discloses an eleventh solution means according to any one of the sixth to ninth solution means in which a part or all of moisture separated from the compressed air by the demoisturizing means (22) is supplied, together with low-temperature air from the expansion device (23), into the room.
Further, the present invention discloses a twelfth solution means according to the ninth solution means in which a part or all of moisture separated from the compressed air by the demoisturizing means (22) is supplied to the exhaust air by the moisturizing means (41, 42).
Further, the present invention discloses a thirteenth solution means according to any one of the sixth to twelfth solution means in which the separation membrane is composed of a polymeric membrane and formed so as to allow water vapor to pass therethrough by water-molecule diffusion in the membrane.
Further, the present invention discloses a fourteenth solution means according to any one of the sixth to twelfth solution means in which the separation membrane has a large number of pores having a size equal to a molecule free path and is formed so as to allow water vapor to pass therethrough by water-molecule capillary condensation and diffusion.
Further, the present invention discloses a fifteenth solution means according to any one of the first to fourteenth solution means in which the compressor (21) is so formed as to draw in room air and supply air that is supplied from the outside to the inside of the room.
Finally, the present invention discloses a sixteenth solution means according to any one of the first to fifteenth solution means in which low-temperature air from the expansion device (23) is mixed with room air and thereafter the mixture is-supplied into the room.
In the first solution means, the compressor (21) compresses at least room air which then becomes high-pressure, compressed air. The compressed air is cooled in the cooling means (30) and thereafter expanded in the expansion device (23) to become low-temperature air. The low-temperature is supplied into the room for cooling thereof. Here, the temperature of exhaust air expelled from inside the room for the purpose of ventilation et cetera is approximately the same as room temperature, therefore being lower than outside air temperature. In the present solution means, in the cooling means (30) compressed air is cooled with exhaust air the temperature of which is lower than that of outside air.
Further, in the second solution means, the moisturizing means (41) supplies moisture to -exhaust air, so that the temperature of the exhaust air is made lower than that of room air by evaporation of the moisture supplied. And then, in the cooling means (30), the exhaust air, the temperature of which is lower than room temperature, is subjected to heat exchange with compressed air.
Further, in the third solution means, the moisturizing means (42) supplies moisture to exhaust air and the cooling means (30) utilizes a sensible heat of the exhaust air and a latent heat of vaporization of the moisture for compressed air cooling. That is, in the cooling means (30), the compressed air is cooled while on the other hand the exhaust air is heated, and the moisture supplied to the exhaust air is evaporated. At that time, the temperature rising of the exhaust air is suppressed by such moisture evaporation, thereby maintaining a difference in temperature between the exhaust air and the compressed air.
Further, in the fourth solution means, the moisturizing means (41, 42) supply a possible maximum amount of moisture to exhaust air in such a range that no condensation occurs in the exhaust air when it is expelled from the cooling means (30). Accordingly, compressed air cooling is carried out by making utilization of a latent heat of vaporization of the moisture to the full extent.
Further, in the fifth solution means, moisture is gradually supplied, through a specified moisture permeable membrane, to exhaust air by the moisturizing means (41, 42).
Further, in the sixth or eighth solution means, the demoisturizing means (22) removes moisture from the air compressed in the compressor (21). At that time, since the demoisturizing means (22) has a specified separation membrane, moisture in the compressed air is removed therefrom, still remaining in the form of water vapor.
Further, in the seventh or ninth solution means, depressurization provided by the depressurizing means (36) ensures creation of a difference in partial pressure of water-vapor between both the sides of the separation membrane. That is, one surface of the separation membrane comes into contact with compressed air and the other surface is subjected to depressurization by the depressurizing means (36). Accordingly, the partial pressure of water-vapor of the other surface side of the separation membrane is held lower than that of the compressed air.
Further, in the tenth solution means, one surface of the separation membrane is brought into contact with compressed air and the other surface thereof is brought into contact with exhaust air. Accordingly, in a running condition in which the exhaust air is lower in partial pressure of water-vapor than the compressed air, moisture in the compressed air travels to the exhaust air without any external action.
Further, in the eleventh solution means, moisture separated from compressed air is used for room humidification. Here, if moisture is separated from compressed air, this may result in gradual drop of the room humidity. On the other hand, in the present solution means, a part or all of moisture separated is brought back into the room, thereby providing protection against excessive drop in the room humidity.
Further, in the twelfth solution means, moisture separated from compressed air is supplied to exhaust air by the moisturizing means (41, 42) and a latent heat of vaporization of that moisture is utilized for cooling of compressed air in the cooling means (30).
Further, in the thirteenth or fourteenth solution means, the separation membrane is so formed by a given process so that it allows water vapor to pass therethrough.
Further, in the fifteenth solution means, supply air that is supplied from the outside to the inside of a room is supplied, together with room air, to the compressor (21). The supply air is for ventilation and the temperature of the supply air is substantially the same as outside air temperature. Together with the room air, the supply air flows through the compressor (21), through the cooling means (30), and through the expansion device (23) in that order. After it is cooled, the supply air is supplied into the room.
Further, in the sixteenth solution means, even when the temperature of the low-temperature air becomes considerably low depending upon the running condition, the low-temperature air is mixed with mixing air, whereby the temperature of the low-temperature air when it is supplied into the room will not become that low.
In accordance with the above-described solution means, compressed air cooling is carried out using exhaust air. This makes it possible to cool the compressed air to lower temperatures when compared to cooling with outside air. Because of this, it is possible to achieve reduction in the input to the compressor (21) while maintaining cooling capacity, thereby providing an improved COP.
In respect to the above point, a description will be given with reference to a graph of FIG. 3. First, when compressed air is cooled with outside air, it is required that compression ratio be increased so that the compressed air becomes able to give off heat to the outside air. More specifically, it is required that the air be compressed from Point A to Point Bxe2x80x2, and a compression work of the compressor (21) is Wcomxe2x80x2. The compressed air is cooled from Point Bxe2x80x2 to Point Cxe2x80x2 and thereafter subjected to expansion from Point Cxe2x80x2 to Point D in the expansion device (23), thus becoming low-temperature air. At that time, a recovery work of the expansion device (23) is Wexpxe2x80x2. Therefore, the input required is (Wcomxe2x80x2xe2x88x92Wexpxe2x80x2).
On the other hand, when compressed air is cooled with exhaust air the temperature of which is lower than that of outside air, this enables the compressed air to give off heat to the exhaust air even at low compression ratio. More specifically, compression of the air from Point A to Point B will suffice, and a compression work of the compressor (21) is Wcom. The compressed air is cooled down from Point B to Point C and thereafter subjected to expansion from Point C to Point D in the expansion device (23), thus becoming low-temperature air. At that time, a recovery work of the expansion device (23) is Wexp. Therefore, the input required is (Wcomxe2x88x92Wexp).
Accordingly, if compressed air is cooled with exhaust air, this reduces the required input from (Wcomxe2x80x2xe2x88x92Wexpxe2x80x2) to (Wcomxe2x88x92wexp). In both of the cases, the cooling capacity is Qref. Here, COP is found by dividing cooling capacity by input. Accordingly, the arrangement that compressed air is cooled with exhaust air makes it possible to achieve reduction in the input while maintaining cooling capacity, thereby achieving an improved COP.
Further, in accordance with the second solution means, it is possible to perform cooling of compressed air with exhaust air whose temperature has been further lowered in comparison with room temperature. Because of this, it is possible to cool the compressed air to further lower temperatures, thereby achieving a further improved COP.
Further, in accordance with the third solution means, it is possible to suppress the temperature rising of exhaust air in the cooling means (30) by evaporation of the moisture supplied. This makes it possible to maintain a temperature difference between the exhaust air and the compressed air, therefore promoting the transfer of heat from the compressed air to the exhaust air. As a result, it is possible to cool the compressed air to a further lower temperature, thereby achieving a further improved COP.
Further, in accordance with the fourth solution means, moisture evaporation latent heat is utilized to the full in such a range that no condensation occurs in the exhaust air, for compressed air cooling. Because of this, it is possible to cool compressed air by making utilization of moisture evaporation latent heat without the necessity to process drain water.
Further, in accordance with the fifth solution means, moisture is supplied little by little to the exhaust air, thereby ensuring that the moisture supplied is evaporated positively in the exhaust air. As a result, the moisture supplied into the exhaust air will not remain in the phase of liquid. Accordingly, moisture evaporative latent heat is utilized to the full for compressed air cooling without taking into consideration the processing of drain at all.
Further, in accordance with the sixth or eighth solution means, it is possible to deliver, after separation of moisture from compressed air, the compressed air to the expansion device (23). This makes it possible to provide expansion of the compressed air that does not contain therein much moisture, thereby preventing the occurrence of condensation in the post-expansion low-temperature air. As a result, it becomes possible to perform room cooling while preventing emission of liquid droplets together with low-temperature air into the room.
Further, in accordance with the present solution means, it is possible to separate moisture from the compressed air in the form of water vapor without the occurrence of condensation. As a result, it is possible to increase cooling capacity, thereby achieving an improved COP.
In respect to the above point, a description will be given with reference to a graph of FIG. 4. First, when moisture is not removed from the compressed air, a refrigeration cycle in such a case is indicated by Point A, Point B, Point Cxe2x80x2, and Point Dxe2x80x2, and the cooling capacity is Qrefxe2x80x2. On the other hand, when moisture is separated from the compressed air in the form of water vapor, it is possible to lower the enthalpy of the post-cooling compressed air by enthalpy held by the separated water vapor. More specifically, the compressed air can be placed in the state of Point C and a refrigeration cycle in this case is indicated by Point A, Point B, Point C, and Point D, and the cooling capacity is Qref. Both the cases are substantially identical not only in the compression work of the compressor (21) but also in the recovery work of the expansion device (23), so that the input varies little. Accordingly, it is possible to increase the cooling capacity from Qrefxe2x80x2 to Qref without increasing the input, thereby achieving an improved COP.
Further, in accordance with the seventh or ninth solution means, it is possible to ensure, in any operating condition, a difference in partial pressure of water-vapor between both the sides of the separation membrane by the depressurization means (36). Accordingly, it is possible to separate water vapor from the compressed air at all times by the separation membrane, thereby making it possible to provide stable running operations while achieving an improved COP. Further, even during start-up it is possible to ensure a difference in partial pressure of water-vapor between both the sides of the separation membrane. Accordingly, in accordance with the present solution means, it is possible to shorten the time taken to achieve sufficient cooling capacity from the start time.
Further, in accordance with the tenth solution means, it is possible to expel water vapor separated from compressed air to the outside of the room, together with exhaust air. This eliminates the need for a structure for processing the water vapor separated, therefore achieving structure simplification.
Further, in accordance with the eleventh solution means, it is possible to provide protection against excessive drop in room humidity, thereby making it possible to maintain not only room temperature but also room humidity in specified ranges to improve the comfortability of the person present in the room.
Further, in accordance with the twelfth solution means, it is possible to use moisture separated from compressed air for cooling of the compressed air in the cooling means (30). As a result, it becomes possible to reduce the amount of water required for running operations.
Further, in accordance with the thirteenth or fourteenth solution means, it is possible to ensure that a separation membrane having a specified function is formed positively.
Further, in accordance with the fifteen solution means, it is possible to perform operations in which both room air and supply air are used as a refrigerant.
Further, in accordance with the sixteenth solution means, it is possible to prevent the temperature of air that is emitted into the room from becoming too low, thereby maintaining the comfortability of the person present in the room.